Hemophiliacs with symptomatic disease are multiply exposed to blood products including factor concentrates to correct the Internet clotting factor deficiencies. Prior to routine use of heat inactivation and screening of donor blood for specific viral pathogens, hemophilia patients were routinely exposed to, and infected with, viruses such as hepatitis B (HBV), hepatitis C (HCV) and human immunodeficiency virus (HIV). Cohort studies in hemophiliacs suggest several clinically and scientifically important findings that warrant further detailed investigation including; a) Liver disease progression may be altered in hemophiliacs infected with HCV with more rapid progression to liver failure and death; b) The source of infection from large pools of concentrate that were potentially infected by multiple discreet donors leads to a high risks of mixed infection represented by both genotype and quasi species heterogeneity; c) The HIV coinfected hemophiliacs may have different clinical outcomes and an altered immune response may facilitate our understanding of the underlying process of mutant virus selection, and the associated clinical outcomes. The overall goals of this proposal include the study and characterization of the genomic RNA of HCV in infected hemophilic patients with and without confection with HIV. In the retrospective Phase 1, we utilize the NCI Multi center Hemophiliac Cohort Study serum bank database to study the relationship between progression to decompensated liver disease and quasi species variability in the viral envelope hyper variable and core domain. Heteroduplex analysis will be used to rapidly screen samples from index patients and matched controls using samples longitudinally collected over a 10 year or longer period of time. Peptides will be produced from unique quasi species and these peptides will be evaluated for their function as CTL epitomes. Phase 2 involves the initiation and performance of a clinical intervention trial designed to determine variable kinetic response rates to PEG-interferon+ribavirin between hemophiliacs with HCV alone vs HCV/HIV coinfected subjects. Quasi species populations will be modified/cloned, sequencing will be performed to generate families of closely related core peptides that will be studied for their ability to bind and stimulate an immune response. Treatment nonresponders will be followed in a prospective cohort study for up to 3 additional years so that the evolution of the virus, and its associated immune response in this group can be evaluated.